Method of welding polyurethane thin film

ABSTRACT

A method of welding at least two layers of a thin thermoplastic polyurethane elastomer (10A,B) to form a weld seam (12) to produce polyurethane barrier products such as, but not limited to, gloves (20), condoms (30), inflatable catheter balloon cuffs (48A,B), ostomy pouches (50), organ bags (60), and instrument covers (70) through a process of pre-heating a sealing die platen, the at least two layers of the polyurethane (10A,B) softened while under pressure from the preheated die platen, followed by welding the at least two layers of polyurethane (10A,B) film by transmission of a radio-frequency energy to the film (10A,B) to produce a weld seam (12) and then allowing the weld seam (12) to cool, the resultant product having seam integrity.

This is a divisional of application Ser. No. 08/104,666, filed Aug. 11,1993, now U.S. Pat. No. 5,469,863.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a new method of joining by a weldingprocess, at least two layers of a thin polyurethane thermoplasticelastomer film having a thickness in the range of 0.5 to 5.0 mils(0.0127 mm to 0.127 mm), without wrinkling, causing pin-holes orholidays and without burning or charring the material. Such weldedpolymer films are employed to make gloves, including industrial andmedical gloves, condoms, organ bags for endoscopic surgical procedures,catheter balloons, and barrier structures to isolate articles, includingmedical and surgical instruments from environmental contamination,infectious material and the like.

2. Description of Background and Other Information

Natural rubber sheet and film, formed by coagulation of natural rubberlatex, have long been employed to form barrier and environmentalprotective products, such as surgical gloves, condoms, and the like.

In the medical and surgical field, there is a substantial need foreffective and reliable infection and contaminant-control barrierproducts, primary among which are surgical gloves. These products mustnot leak or rupture nor must there be any breach of the barrier materialthrough porosity, permeability or structural weakness. Desirably, suchproducts should provide protection against accidental cuts and needlesticks, and the like. A long shelf life before use is important, as arephysical properties such as resistance to tearing, solvents and otherenvironmental exposure. These features should desirably be attained inproducts which are thin enough to present minimal interference withtactile sensing and mobility.

Industrial gloves and related barrier apparel and clothing and the likehave similar requirements.

Condoms are of increasing importance in the prevention of the spread ofAIDS viruses, other sexually transmitted diseases, and for effectivecontraception.

The use of containment for excised tissue and organs in surgicalprocedures is also of increasing import in the medical field,particularly in the fast growing field of endoscopic examination andsurgery. For example, in the removal of a gall bladder, appendix orother organ or tissue suitable to an endoscopic approach.

Catheter balloons are important in procedures such as angioplasty and inthe use of in-dwelling catheters, endotracheal tubes and other deviceswhere an inflatable cuff is required.

Barrier containment for implantable devices, such as cardiac pacemakersand the like, and for surgical instruments inserted into the body duringsurgical procedures is another area of increasing importance. Forexample, difficult to clean and sterilize instruments such asliposuction cannulae, endoscopic instruments and other lumen containingand complex instruments where cleaning and sterilizing may beunreliable.

These are products which require thin film or sheet materials, and arefrequently made of natural rubber or "latex" film and sheet materials.

Latex sheet or film is normally a porous material with a certain amountof permeability. Latex products are often formed through a dippingtechnique which, as the latex becomes thinner or is stretched, resultsin an increase in porosity and permeability. Comparable limitationsapply to milled sheets formed on rolling or rubber mills. Certainchemicals and molecules, up to the size of AIDS viruses, can permeatelatex without causing rupture or displacement, an undesirablecharacteristic in barrier protection. Latex cannot provide barrierintegrity for devices such as surgical gloves and condoms where barrierprotection is of prime importance.

Latex also has limited tensile strength and tear resistance and ishighly susceptible to cuts and punctures. In addition, the material hasa limited shelf life, and will become more fragile and brittle overtime.

In today's society, barrier products require maximum protection toprevent the spread of pathogenic organisms as well as the preventingcontamination of otherwise clean or sterile materials or devices. Latexproducts cannot provide this quality of protection because of materialfaults inherent in the material formed by available techniques.

There is an increasing proportion of the population of potential latexusers, particularly workers in the medical and related fields, that areunable to use latex products because of an allergenic reaction thatcontact with latex products produce in sensitive individuals. Increasingreports are appearing in the medical literature of anaphylactic shockreactions attributed to exposure to latex products, as well as lessserious but quite irritating contact dermatitis. As a result of thefrequency and severity of such problems, OSHA regulations and guidelineshave recently been established requiring employers to provide workersexposed to blood borne pathogens with an adequate hypo-allergenicsubstitute or other effective alternatives to contact with naturalrubber latex products.

In addition, the contact dermatitis that occurs as a result thecustomary employment of lubricants and powders with latex products canbe severe, painful and require treatment.

Synthetic polymer elastomers are finding a greater use in applicationstraditionally supplied by latex for rubber goods, both in themedical/surgical fields, and in a variety of commercial and industrialapplications.

It has been recognized that polyurethane polymers have propertiesdesirable for many of the rubber goods heretofore made of naturalrubber, particularly thermoplastic elastomer polyurethanes.

There has been considerable effort in the industry to provide barrierdevice products of polyurethane materials as a substitute for latex, butuntil now, no cost effective and fully reliable method to produce suchproducts has been available.

The dipping technique employed for many natural rubber latex productscan be employed with polyurethanes, but have not attained all theadvantages and benefits desired. For example, dipping processes areexpensive, because of the expensive solvents and the attendantenvironmental and atmospheric pollution and fire and health concernsrequired to form and deal with dipping solutions of polyurethanes, whilethe nature of dipping processes does not produce optimal film propertiesin any event. It is difficult to attain dip molded films which arereliably free of pin holes and porosity. It is also difficult to achieveuniform film thicknesses required of a number of uses.

Some polyurethane products are formed by joining polyurethanes with theuse of adhesive bonding or welding techniques. However, most effectiveadhesives are poorly tolerated or are completely intolerable in manycontexts of use, and are time and labor intensive operations, whilewelding techniques have been limited to joining layers of polyurethanehaving a thickness of no less than about 5 mils (0.127 mm).

Until the present invention, the welding of thin layers of polyurethanein the range of 0.5 to 5.0 mils (0.0127 to 0.127 mm) resulted inwrinkles, pin holes, discontinuities, holidays and burn or charringdefects. The use of thin polyurethane film has been precluded because ofthe lack of a safe and a reliable welding method that preserved theintegrity of the seam formed by the weld while creating a seam that wasof high quality acceptable to users.

The joining of polyurethane to form a seam is well known in the art.Methods such as adhesive bonding, electromagnetic bonding, hot platewelding, induction bonding, insert bonding, radio-frequency sealing,spin welding, thermostacking, ultrasonic sealing and vibration weldinghave all been described in the literature. None of these methods,however, provide a secure, reliable and reproducible seam where thepolyurethane is in the form of a film with a thickness in the range of0.5 to 5.0 mils (0.0127 to 0.127 mm) and, therefore, are not applicableto polyurethanes less than 5 mils (0.127 mm) in thickness. As those ofordinary skill in the art will recognize, these are the very dimensionsof greatest interest in a very substantial proportion of uses andproducts.

Generally, the welding of thin polyurethanes, due to the thinness andbroad melting point temperature of the material, resulted in severalproblems, including:

1) film wrinkling during welding;

2) seam pin holes or holidays;

3) too broad of a seam;

4) arcing, charring and burn marks of the polyurethane;

5) risk to the manufacturing operator; and

6) unacceptable levels of failure in use.

There are several problems with current joining, bonding or weldingmethods in their application to thin polyurethanes. For example, withconventional heat sealing equipment, it is difficult to controltemperature accuracy due to a temperature rise with a longer time use.Because of this lack of temperature uniformity critical in thin filmjoining, wrinkling, pin holes or holidays can occur in the seam.

Electromagnetic bonding for thermoplastic substrata is based on theprinciple of induction heating: a composition consisting offerromagnetic particles dispersed in a polymer matrix develops heat whensubjected to a high-frequency alternating current source. When thiscomposition is placed between two synthetic polymer elastomers, the heatdeveloped is used to rapidly fuse the abutting surfaces. The techniqueis limited to thick structures, greater than 5 mils in thickness. Inmany contexts, the presence of ferromagnetic particles is unacceptable.

Impulse heating creates an unacceptably broad seal. When the material tobe sealed is thin, pin holes and holidays result due to uneven and poortemperature control. A sufficient seal cannot be assured andreproducibility is poor.

Radio-frequency welding is also known as R.F. heat sealing,high-frequency sealing, or dielectric heat sealing. A radio-frequencywelder directs a large amount of radio frequency energy into the seamarea. The energy causes the molecules of the material to oscillate orvibrate, creating heat. A combination of this heat, and pressure exertedby the pressure component of the welder, causes the materials to fusionbond. The ability and ease at which materials bond is related to theirdielectric properties. Radio-frequency bonding works well when thethickness of a thermoplastic polyurethane elastomer film is greater than5.0 mils (0.127 mm) although the energy intensity required is ratherhigh. In thin film applications, sparking occurs due to arcing which cancause burns and chars to the film. This can also be hazardous to theoperator. Radio-frequency welding is not widely employed withthermoplastic polyurethane elastomers because of these limitations.

The most commonly used application of radio-frequency welding is inpolyvinyl chloride bonding and embossing in which the melting of thematerial brought about by molecular vibration. Molecules within thematerial are subject to periodic stresses caused by a radio frequencyfield alternating in polarity several million times per second, mostoften at 27.12 MHz. The amount of heat developed in the material isdirectly proportional to the amount of radio-frequency power applied toit. If the material has a high dissipation factor, that enables a risein temperature in a radio-frequency field, when the heat exceeds themelting point of the material under pressure, and such a melt, undercontrol, can be employed to form a fusion bonded joint or weld.

Until now, it has not been possible to convert, particularly forsurgical and medical use, the excellent properties of thin thermoplasticpolyurethane elastomer materials with a thickness of less than 5 mils(0.127 mm) into effective rubber goods. While polyurethane has beenavailable for many years, the ability to produce thin polyurethane safeand usable barrier products having acceptable seam integrity has notbeen available. Polyurethanes have properties superior to latex,including structural strength, elasticity and the absence of porosityand permeability.

U.S. Pat. No. 4,463,156 to McGary, Jr. et al., "Polyurethane Elastomerand an Improved Hypoallergenic Polyurethane Flexible Glove PreparedTherefrom", discloses a soft, low modulus, non-crystalline segmentedpolyurethane glove comprised of specific chemical and physicalcharacteristics that result in a more comfortable and easier to usesurgical glove. McGary, Jr. et al. do not suggest or teach a method ofjoining two layers of thin polyurethane film to form a weld seam throughthe process of radio-frequency welding in glove fabrication.

U.S. Pat. No. 3,148,235, "Method of Making Plastic Gloves", and U.S.Pat. No. 3,197,786, "Plastic Gloves" to Velonis, disclose a method formaking a seamless plastic glove and the glove itself, formed from a filmof a fused polyvinyl chloride resin by utilizing dipping forms made fromaluminum. The method and product of Velonis does not suggest or teach amethod of joining two layers of thin polyurethane film to form a weldseam through radio-frequency welding in glove fabrication.

U.S. Pat. No. 4,684,490 to Taller et al. "Process for Preparation ofPolyurethane Condoms", discloses a polyurethane condom formed through adipping method in which the polyurethane is in the form of an organicsolvent solution. The process of Taller et al. does not anticipate orteach a method of joining two layers of thin polyurethane film to form aweld seam through radio-frequency welding in condom fabrication.

U.S. Pat. No. 3,553,308 to Kobayashi et al., "Method for PreparingPolyurethane Molded Articles", is a method in which articles,particularly condoms, are prepared by alternately dipping a condom mold,at a controlled speed, in a polyurethane prepolymer solution and thencuring the solution. Kobayashi et al. do not teach or suggest a methodof joining two layers of thin polyurethane film to form a weld seamthrough radio-frequency welding in fabricating a condom.

U.S. Pat. No. 4,576,156 to Dyck et al., "Prophylactic Device andMethod", discloses a method of preparing a condom in which athermoplastic polyurethane elastomer material is deformed using apreformed mandrill in which a vacuum is applied to the system during thedeformation step. Dyck et al. does not teach or suggest a method ofjoining two layers of thin polyurethane film to form a weld seam throughradio-frequency welding in producing a condom.

U.S. Pat. No. 3,094,704 to Abildgaard, "Plastic Glove", discloses aseamless plastic glove made from a skin-fitting form-mold plastic layeris produced from an elastomer by spraying a molten or dissolved plasticmaterial on a plurality of molds or forms. Abildgaard does not teach orsuggest a method of joining two layers of thin polyurethane film to forma weld seam through radio-frequency welding in the production of gloves.

As has been noted, seam integrity is an essential and critical parameterfor barrier devices in preventing the transmission of microscopicparticles or for special sensor devices to prevent electrolytetransmission prematurely.

SUMMARY OF THE INVENTION

We have found that highly efficient R.F. welding of thermoplasticpolyurethane elastomers is attained by heating the polymer to atemperature above the Vicat softening temperature (but below the heatdistortion temperature or film distortion temperature), and subjectingthe heated polymers to be joined to R.F. energy and pressure. Theinvention is particularly useful for joining thin films of thepolyurethane, particularly films of 0.5 to 5.0 mils (0.0127 to 0.127mm).

The R.F. welding technique is employed to fabricate a variety of medicaland industrial products, including gloves, condoms, catheter balloons,containments for implantable medical appliances and devices, endoscopictissue and organ containment bags, cavity liners for surgical andmedical implements such as liposuction cannulae, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and additional objects, characteristics, and advantages of thepresent invention will become apparent in the following detaileddescription of preferred embodiments, with reference to the accompanyingdrawings.

FIG. 1 is a top view of two welded thin film layers of a thermoplasticpolyurethane elastomer material.

FIG. 2 is a side view of two welded thin film layers of a thermoplasticpolyurethane elastomer material.

FIG. 3 is a broad view of a thermoplastic polyurethane elastomer glove.

FIG. 4 is a side view of a thermoplastic polyurethane elastomer glove.

FIG. 5 is a side view of a thermoplastic polyurethane elastomer condom.

FIG. 6 is a view of the reservoir end of a thermoplastic polyurethaneelastomer condom.

FIG. 7 is a view of an non-inflated thermoplastic polyurethane elastomerballoon cuff of an in-dwelling urinary bladder catheter.

FIG. 8 is an inflated thermoplastic polyurethane elastomer balloon cuffof an in-dwelling urinary bladder catheter.

FIG. 9 is a thermoplastic polyurethane elastomer ostomy pouch.

FIG. 10 is a side view of a thermoplastic polyurethane elastomer organbag.

FIG. 11 is an open-top view of a thermoplastic polyurethane elastomerorgan bag.

FIG. 12 is a surgical instrument.

FIG. 13 is a thermoplastic polyurethane elastomer instrument cover.

FIG. 14 is a surgical instrument partially inside of a thermoplasticpolyurethane elastomer instrument cover.

DETAILED DESCRIPTION OF THE DRAWINGS AND PREFERRED EMBODIMENTS

The present invention is a new method of making rubber goods from thinlayers of thermoplastic polyurethanes and the thin thermoplasticpolyurethane rubber goods to be used as barrier products and devices ina variety of medical, commercial and industrial fields. The products ofthis new method have high integrity, and are free from wrinkles, pinholes, holidays, burns or charring, mandatory in devices of this class.

This new method combines the use of heat from a preheated die platenwith a radio-frequency welding technique to create a uniform weld seamin a thin polyurethane film material having a thickness in the range of0.5 to 5.0 mils (0.0127 to 0.127 mm).

In using contact conduction heat-sealing equipment, heat is transferredfrom the edge of the outer layer to the inner layer of the film. Thistypically results in a temperature gradient in the two layers of filmwith a difference in temperature between the layers. When used on thinfilm, a wrinkling occurs at the seam accompanied by the formation of theformation of pin holes and holidays due to the uneven heat. The thinnessof the film exacerbates the effects.

In using the technique of radio frequency welding alone, heating takesplace throughout the polymer layer. The molecular layer at the interfaceof two layers becomes excited and generates heat. Once the energy isinput the heat raises the temperature to the fusion point, thus creatingthe seam in conjunction with applied pressure. Because the effectoperates at the molecular level, radio-frequency welding achievesexcellent seam integrity and the technique is sometimes used forpolyurethane film thicknesses greater than 7.0 mils (0.177 mm) inthickness. However, in the film thickness range of 0.5 to 1.5 mils(0.0127 to 0.0381 mm), there is very slow absorption of theradio-frequency energy required to give enough heat to achieve seamintegrity becuase of the microcrystalline character of the polymer. Atthe required radio-frequency energy level, the energy will induce thearcing and spark that results in burn holes in thin film. It can alsocreate a char, and may damage the die platen itself. R.F. welding ofthin polyurethane films, less than about 5 mils in thickness, is notemployed for these reasons.

In the broadest terms, the present invention is based on the discoverythat R.F. welding of thermoplastic polyurethanes, and in particular,thermoplastic polyurethane elastomers, is highly efficient if conductedabove the polymer Vicat softening temperature. Thus, preheating thepolymer to an appropriate temperature, placing polyurethane parts to bejoined in joining configuration under pressure, and applyingradio-frequency energy to the joint region can be effectively andefficiently employed to form high quality welded joints at greaterefficiency and economy than has heretofore been possible.

It is, of course, apparent that the invention has its greatest utilityin the welding of very thin films of thermoplastic polyurethane, on theorder of 0.5 to 5.0 mils (0.0127 to 0.127 mm) in thickness, which havenot been amenable to effective and reliable welding by other techniques,including normal R.F. welding procedures. Thus, while the technique isequally applicable to thicker films and other forms of such polymers,the present invention is hereafter discussed with primary reference tothe fabrication of welded joints and seams between these very thinfilms.

Most molecules are polarizable in an electric field. The degree ofpolarization, and the energy required to achieve it, is controlled bythe dissipation factor or loss factor of a material. A material that isreadily polarized by a small electric field has a high loss factor andis easy to heat.

As polarizing field alternates direction at a high frequency,considerable energy can be imparted to each molecule of the material. Avery large number of materials are resonant at the usual frequency of27.12 MHz commonly employed for R.F. welding. Thermoplasticpolyurethanes are no exception.

This energy appears as heat. Since the electrical field penetrates thematerial, the heat is generated within the material and radiates ortransfers outwardly.

The amount of heat generated without arcing or interior scorching isdependent on the dielectric properties and the "dissipative factor" and"loss index" of any particular material.

Following equation defines the power input and rate of heat generation:

    P=2π f E.sup.2 Cε' tan σ

wherein:

P=power input in W

f=frequency (normally, 27.2 MHz for R.F. welding)

E=field strength or voltage between the electrodes Kv

C=capacitance of the material in pF

ε'=dielectric content

tan σ=the loss factor

(ε')×(tan σ)≡dissipation factor (for σ≧loss index)

The higher the loss index, the easier a material is to heat.

Thick (8 mil and above) plasticized polyvinyl chloride film is wellknown to be suitable but not optimal for R.F. welding techniques. Thickpolyurethane films are welded by R.F. energy. However, polyurethanefilms require three to four times more power than polyvinyl chloridefilms of comparable thickness.

These differences in power input requirements stem from several majorfactors:

Polyvinyl chloride has the readily polarizable Cl group on the polymerchain. Polyurethanes do not commonly have such substituents.

In addition, polyvinyl chloride is highly plasticized in almost all itscommon forms while polyurethanes--particularly in film form--generallyare not plasticized at all or have modest levels of such additives.

Polyurethanes in the form of thermoplastic elastomers are dependent onmicrocrystalline domains to provide their elastomeric properties. Theamount of such microcrystallinity is variable with processing techniquesand is generally highest in films, ordinarily formed by blowingtechniques. The blown films are more highly ordered and oriented by thestretching of the film during blowing. The thinner the film, the higherthe microcrystalline content of the film.

The crystalline domains have low dissipation factors which increases theR.F. energy input required for heating. The heat input requirements aredirectly proportional to the amount of microcrystallinity. During R.F.heating, a substantial component of the input is required to raise thetemperature of the crystalline domains to an adequate temperature toachieve a dissipation factor comparable to the amorphous regions in thepolymer (at and above the Vicat softening temperature).

Typically, a polyurethane thermoplastic elastomer film will require apower input three times higher than a polyvinyl chloride film ofcomparable thickness to attain R.F. welding bonds. Attempting to do soat high energy input results in qualitative problems of arcing,sparking, charring, bond discontinuities or "holidays" and the like.

While many of the difficulties could be resolved by reducing the energylevel of the R.F. input, the time to achieve bonding temperatures ismaterially and unacceptably increased, and the productivity of R.F.welding and the justification for the capital costs is lost.

In our invention, the thermoplastic polyurethane elastomer is heated toa temperature above the Vicat softening temperature of the polymer priorto the R.F. welding procedure. The Vicat softening temperature of suchelastomers is ordinarily in the range of about 60° C. to 150° C. Thesetemperatures are conveniently attained by a wide variety of techniques,from preheating the material in an oven, to passing the material,particularly in film form, under infrared heat lamps, to conducting theR.F. welding with a heated platen and die. The latter is generallypreferred, since it permits heating the materials to be welded only atthe seam areas and their immediate vicinity, minimizing the heat input.

With the film heated above the Vicat softening temperature, R.F. weldingproceeds rapidly and efficiently at low R.F. energy levels, as a resultof the high dissipation factor provided by the preheating. The increseddissapation factor is attributable to melting of the crystallinedomains. In amorphous form at high temperatures, above the Vicatsoftening temperature, the polyurethanes have high dissipation factors.At the low R.F. energy levels, there is no arc formation, no sparking orcharring, and bond discontinuities are readily prevented.

The qualitative properties of the weld seams formed by the presentinvention are consistently and reproducibly excellent. There are alsosignificant reductions in out-of-spec weld joints. Quantitatively, theproductivity of the operation is excellent and the energy usage andcosts are reduced.

The thermoplastic polyurethane elastomers to which the present inventionis applicable are well characterized in the literature, familiar tothose of ordinary skill in the art, and are widely available from anumber of commercial sources. A variety of such materials are availablein medical and food grades. Those of ordinary skill in the art are wellable to select appropriate materials for their intended use. The presentinvention is applicable to such materials.

In the present invention, a combination of dry heat and radio-frequencywelding is used to create a seam without breach or deformation. Inusage, the method may typically comprise the following steps:

(1) The welding die platen is preheated to a temperature above the Vicatsoftening temperature of the polyurethane elstomer, typically between60° C. to 150° C., depending on the nature of the polymer. It isappropriate to keep the temperature below the film deformationtemperature. At these temperatures, the die will not stick to thepolyurethane film but will provide enough external heat to pre-heat thefilm and prepare it for welding.

(2) Layers of a thin film are fed through an R.F. heat welder, the twolayers ultimately having direct heat transfer contact with the dieplaten just prior to and during the welding operation.

(3) The two layers of thin film are subjected to die platen pressure.Pressure, typically in the range of 50 to 80 pounds per square inch(psi), is exerted at least on the seam area of the two layers.

(4) A surge of low power radio-frequency energy is directed by thewelder into the seam area of the two layers of film when the pressurefrom the die platen is exerted on the material. The radio-frequencyenergy range is generally from 1.0 to 6.0 kW, proportional to thethickness of the thermoplastic film. It is transmitted for a duration ofabout 1.0 to 2.0 seconds.

The preheated film is excited at the inner molecular surface at this lowenergy level causing a weld which produces a seam with integrity.Because of the relatively low energy required, the film is notoverpowered or overheated, thereby avoiding sparking or burning of thematerial. By using this method, it is possible to eliminate the excessheat generation of either the standard contact heat sealing machine orthe impulse-heat machine. It also eliminates sparking caused byradio-frequency at higher energy levels.

Combining these two operations results in a wrinkle free, thin, weldseam with excellent integrity, only attainable in the past withradio-frequency welding techniques on thicker materials. Preparing thetwo layers of film for welding by applying heat to raise the temperatureabove the Vicat softening temperature of the polyurethane film beforetransmitting radio-frequency energy avoids the slow heating associatedwith thermoplastic polyurethane elstomers. Less radio-frequency energyis used and thus sparks and burn marks are avoided.

The use of radio-frequency input can be precisely metered, monitored anddocumented, ensuring seam integrity. This cannot be done with the use ofheat sealing.

Thin thermoplastic polyurethane films for certain applications caninclude a variety of the common forms of compounding componentscustomarily employed with such polymers, including reinforcing fillers,plasticizers or lubricants to give specific properties to the ultimateproduct. These compounding components may be helpful, for example, toprevent blocking or sticking of the film in unwelded areas not subjectedto the seaming operation. In the manufacture of products requiringcompounding components, the compounding components are may be combinedwith the film-forming polymer at the time the film is made. In othercircumstances, the additive may be applied as a coating on the surfaceof the fim prior to welding. In some cases, the additive may be appliedto the welded product, although such techniques are often morecumbersome than the preceeding techniques. The additive materials thatcan be used comprise several types:

(1) antiblocking lubricants are used to prevent sticking between the twopolyurethane layers in organ bags, gloves, instrument covers and thelike. It makes handling from processing to packaging easier and morereliable. Examples of antiblocking-lubricants are fatty acids, esters,amides, bisamides and silica. The amounts of such lubricants istypically about 0.1 to 2% of the polymer weight.

(2) Antistatic agents may be used for rubber goods to be employed in theelectronic industry and with electronic medical appliances and the like.Antistatic properties can be achieved by adding a quaternary ammoniumcompound, for example, such as the Laurostat® HTS series from PPGIndustries, Glycolube® AFA-1 from Lonza, Inc., or Cyastat® LS fromAmerican Cyanamid, Inc.

(3) antimicrobials, biocides, and fungistats and the like are used forsafety in the health care and food industries for reusable products.Representative examples are N-trichloromethylthio phthalimide,10,10'-Oxybisphenoxarsine, and 2-N-Octyl-6-isothiazoline.

(4) UV stabilizers and antioxidants may be used, particularly for rubbergoods which require particularly long shelf life and for re-usableproducts such as gloves. An example of an antioxidant is Irsanox® 0.1 to1% from Geigy, Inc. A useful UV stabilizer is TINUVIN®, also from Geigy.

(5) odorants, deodorants, flavors, pigments, dyes, lakes, opacifiers,brighteners, and the like are used for specific applications.

(6) Radio-opaque fillers are used when it is required to be able toidentify a product through x-ray, as for example in locating an organbag in a body cavity, or as a barrier protection from unintendedexposure to incident radiation. Examples of radio-opaque fillers aremetallic lead, lead oxides, BaSO4, bismuth oxychloride, bismuthsubcarbonate, bismuth trioxide and the oxychlorides, subcarbonates andtrioxides of tungsten.

Small amounts of reinforcing fillers, such as silca, carbon black, andthe like may be employed. The use of such fillers is well known to theart, and do not interfere with the welding in proportions of less thanabout 20 to 25% by weight.

While plasticizers are not often employed with the thermoplasticpolyurethane elastomers, their use does not impair or impede the presentinvention.

The present invention has the objective of providing a new method ofwelding at least two layers of a thin thermoplastic polyurethaneelastomer material, with high levels of seam integrity, for the purposeof creating safer and more durable barrier products not previouslyavailable or available only at unacceptably high costs.

FIG. 1 is a view of joined polyurethane film layers (10A) and (10B)welded together to form a weld seam (12). Weld seam (12) is created bytransmitting radio-frequency energy to preheated film layers (10A) and(10B). In preparation for the welding process, a die platen is preheatedprior to joining film layers (10A) and (10B). Once film layers (10A) and(10B) are brought into contact under from 50 to 80 psi from thepreheated die platen, the film is preheated by conduction from theheated platen in the area to be welded to a temperature above the Vicatsoftening temperature, which will typically be from about 150° to 250°F. (65.5° to 121.1° C.) for most polyurethanes. The preheated filmtemperature should be below the film's melting temperature, preferablyabout 25° F. below the melting temperature, which varies betweendifferent polyurethane materials. The temperature should also be belowthe film distortion temperature.

Radio-frequency energy of 1.0 to 6.0 kW for 1.0 to 2.0 seconds,depending on the thickness of the film, is then transmitted to filmlayers (10A) and (10B) to form a weld seam (12) by fusion bonding of thelayers at their interface. The welded film layers are then allowed tocool.

FIG. 2 is a side view of joined polyurethane film layers (10A) and (10B)of FIG. 1 with weld seam (12). FIG. 2 shows eversion of film layers(10A) and (10B) at weld seam (12). Weld seam (12) has substantiallycomplete continuity and integrity and is without pinholes, holidays orcharred edges. Because film layers (10A) and (10B) are preheated, lessenergy is required at the radio-frequency weld site, thus preventingbreach of the polyurethane film. The strength of the weld has beobserved to be substantially the same as that of the unwelded film. Thespan of the weld seam is thus not a critical parameter, although it willusually be at least two, and preferably 3 to 10 times the thickness ofthe film. Narrower seams make the die more difficult and expensive tofabricate, and make handling of the film feed to the die and platen farmore difficult. Wider seams are also possible, but in most cases arepointless and wasteful of the R.F. and platen heating energies and takelonger to cool.

FIG. 3 is a polyurethane glove (20) comprised of polyurethane filmlayers (24A) and (24B) joined at weld seam (22). Weld seam (22) islocated at the finger contours of glove (20) where the two film layersare joined. The preheated die platen takes on the shape of thepolyurethane product to be created, in this case, a glove shape.Polyurethane film layers (24A) and (24B) are brought into contact underpressure at the welding site and radio-frequency energy is transmittedthus welding film layers (24A) and (24B) to create weld seam (22).

FIG. 4 is a side view of glove (20) with polyurethane film layers (24A)and (24B) joined to form weld seam (22).

FIG. 5 is a male condom (30). Condom (30) is comprised of polyurethanefilm layers (33A) and (33B) joined at wild seam (31). Polyurethanecondoms provide a major breakthrough in barrier protection in preventingthe spread of disease as well as in the prevention of an unwantedpregnancy. The polyurethane film is neither porous nor permeable tochemical or microscopic matter. It is a superior material used inbarrier protection products when compared to natural rubber latexproducts and dipped polyurethanes. The weld seam of the presentinvention has the same strength and integrity as the polyurethane film.

Because of the outstanding properties of the thermoplastic polyurethanefilms and of the welded seams of the present invention, it is possibleto make condoms of thinner films, i.e., on the order of 0.5 to 2 mils,affording particularly enhanced tactile properties and comfort with nodiminution of the required barrier protective and prophylacticproperties. While the polyurethanes are more expensive than naturalrubber, the economies of production in the present invention offset alarge component of the materials costs.

As a result of these features, there is likely to be less resistance tothe use of condoms by those who dislike the reduced tactile sensations.Resistance to the use of condoms is a major impeidment to the preventionof the spread of sexually transmitted diseases and the incidence ofunwanted pregnancies.

FIG. 6 is a view of the reservoir end of male condom (30) with 1.25 milpolyurethane film layers (33A) and (33B) joined to form weld seam (31).Weld seam (31) may be located externally on condom (30). If desired, thecondom may be everted after forming, with the seam on the inside of thestructure. Thin polyurethane film layers of a thickness of 0.5 to 1.5mils (0.0127 to 0.0381 mm) or greater may be used.

The method of the present invention may be employed in the fabricationof both male and female condoms. While the safety and effectiveness offemale condoms is more sensitive to the specific design of the structurethan the male condom, substantially any female condom design can befabricated by the techniques of the present invention, accruing all thebenefits of the improvements of the present invention.

FIG. 7 is a view of a non-inflated polyurethane balloon cuff (48A) of anin-dwelling urinary bladder catheter (40) with film layers (46A) and(46B) joined together at weld seam (44). Balloon cuff (48A) as shown inFIG. 7 is located near the internal end of catheter (40) but may belocated at any site on catheter (40) that would bring it in contact withthe urethra. To inflate balloon cuff (48A), air is injected into aninflation tube (42) which is internally joined to balloon cuff (48A)Balloon cuff (48A) is comprised of polyurethane film layers (46A) and(46B) at weld seam (44). Catheter (40) is inserted into the urinarybladder by way of the urethra to drain urine during prolongedanesthesia, chronic urinary retention, acute retention, to medicallytreat the urinary tract or bladder with fluids and medications, as wellas other uses. The smooth polyurethane surface of non-inflated ballooncuff (48A) allows it to be passed through the urethra to the bladderwith minimum discomfort.

FIG. 8 is a view of an inflated polyurethane balloon cuff (48B) of anin-dwelling urinary bladder catheter (40) with film layers (46A) and(46B) joined together at weld seam (44). Balloon cuff (48B) is inflatedthrough inflation tube (42) which connects internally to cuff (48B).With cuff (48B) inflated, plug (49) is inserted into tube (42) at theopen end of tube (42). Because polyurethane has high strength andintegrity, air cannot inadvertently escape through inflated cuff (48B).

Inflatable polyurethane balloon cuffs are applicable to other insertabletubes where balloon cuff seal integrity is required such as in oral andnasal anesthesia endotracheal tubes, venous and arterial catheters andother such tubes.

Angioplasty catheter balloons may be made by the same techniques. Theexceptional strength of the polyurethane films of the present inventionafford great reliability in such products and the procedures for whichthey are employed.

FIG. 9 is an ostomy pouch (50) comprised of film layers (53A) and (53B)joined at weld seam (51) by the process described in the presentdisclosure. A connecting means (57) of pouch (50) is located at anopen-end (58) of pouch (50). Draw pulls (55) are located beneathopen-end (58) and are drawn when closing off open end (58) at time ofdisconnect of connecting means (57). As a durable and leak-proofmaterial, polyurethane is ideal for this use. Weld seam (51) offersmaximum protection with seam integrity. Pouch (50) size and shape can bedesigned for any specific need.

FIG. 10 is a side view of an organ bag (60) for use in withdrawingtissues excised during endoscopic surgical procedures. The organ bag iscomprised of film layers (64A) and (64B) joined at weld seam (62)through the process described in this disclosure. Bag (60) is funnelshaped with an opening means (68) at open-end (69). A perforations line(67) is located proximal to open-end (69) facilitating separation andremoval of opening means (68), wherein opening means (68), followingseparation, can be removed through an access port in an endoscopicinstrument used to place bag (60). A pair of circumferential draw pulls(66) are located beneath and proximal to perforations line (67). Whendrawn, draw pulls (66) close off open end (69) of bag (60) securing bagcontents and facilitating removal from the surgical situs.

FIG. 11 is an open-top view of organ bag (60) with opening means (68) atopen-end (69). Circumferential draw pulls (66) are located on organ bag(60) at line (65) proximal and beneath perforation line (67). The size,shape and dimension of an organ bag is determined by surgicalrequirements. Polyurethane organ bags are durable, leak-proof, safe andcan be fabricated from thin polyurethane material which facilitatesremoval.

FIG. 12 illustrates a surgical instrument (70) which is difficult toclean and sterilize. Instruments that cannot be disassembled arefrequently difficult or impossible to clean thus exposing surgicalpatients to contamination with possible infection. To protect a patientfrom contamination, instrument (70) is placed into an sterile instrumentcover (71) through open end (77A). FIG. 13 is a view of instrument cover(71) comprised of polyurethane film layers (73A) and (73B), joined atweld seam (75). Cover (71) has an open-end (77A) and an exit-end (77B)Instrument covers can be made in many shapes and sizes to conform toinstrument configurations.

FIG. 14 is a view of instrument (70) inserted into cover (71) throughopen-end (77A). The tip end of instrument (70) extends beyond exit-end(77B) for contact with body tissue. In potentially contaminatedinstruments, a sterile instrument cover offers an extra measure ofprotection to the patient and security to the surgeon.

EXAMPLE 1

The material to be used for a thermoplastic polyurethane elastomer gloveof a thickness of 5 mils (0.127 mm) is selected and fed into anelectronic heat welder. The welding die platen is preheated to about170° F. (76.6° C.). Two layers of thermoplastic polyurethane elastomerfilm are then aligned and brought together under pressure of about 80psi from the die. With the two layers under pressure, and after about 2seconds preheat time, 4.0 kW of radio-frequency energy is transmitted tothe two layers for a period of 2.0 seconds followed by release of thedie platen pressure. A weld seam is created without pin-holes, holidays,charring or burn marks.

EXAMPLE 2

A 1.5 mils (0.0381 mm) thick thermoplastic polyurethane elastomer filmused in the manufacture of a prophylactic condom device is selected. Twolayers of the material are aligned and fed into an electronic heatwelding machine. The die platen is preheated to 200° F. (93.3° C.). Thetwo layers of film are brought together under 65 psi of pressure fromthe die platen. With the two layers of film in contact and underpressure, 2.0 kW of radio-frequency energy are transmitted to the filmto be welded over a 1.0 second period. The weld seam resulting from thewelding process is free of pin holes, holidays, wrinkles or burn marks.

EXAMPLE 3

A 1.2 mils (0.0305 mm) thick thermoplastic polyurethane elastomer filmused in the manufacture of a prophylactic condom device is selected. Twolayers of the material are aligned and fed into an electronic heatwelding machine. The die platen is preheated to 250° F. (121.1° C.). Thetwo layers of film are brought together under 65 psi of pressure fromthe die. With the two layers of film in contact and under pressure, 1.5kW of radio-frequency energy are transmitted to the film to be weldedover a 1.2 second period. The seam resulting from the welding process isfree of pin holes, holidays, wrinkles or burn marks.

EXAMPLE 4

A 0.9 mil (0.0228 mm) thick thermoplastic polyurethane elastomer filmused in the manufacture of a prophylactic condom device is selected. Twolayers of the material are aligned and fed into an electronic heatwelding machine. The die platen is preheated to 250° F. (121.1° C.). Thetwo layers of film are brought together under 55 psi of pressure fromthe die. With the two layers of film in contact and under pressure, 1.2kW of radio-frequency energy are transmitted to the film to be weldedover a 1.0 second period. The weld seam resulting from the weldingprocess is free of pin holes, holidays, wrinkles or burn marks.

Finally, although the invention has been described with reference ofparticular means, material and embodiments, it is to be understood thatthe invention is not limited to the particulars disclosed and extends toall equivalents within the scope of the claims.

What is claimed is:
 1. A method of welding at least two layers of athermoplastic polyurethane elastomer film, comprising the steps of:(a)pre-heating a welding platen to a temperature above a Vicat softeningtemperature and below a thermoplastic elastomer film deformationtemperature of said thermoplastic polyurethane elastomer film, saidthermoplastic polyurethane elastomer film having a thickness in a rangefrom about 0.5 to about 5.0 mils (0.0127 to 0.127 mm); (b) placing atleast two layers of said polyurethane film on the preheated platen, saidplaten heating said thermoplastic polyurethane elastomer film to atemperature above the Vicat softening temperature of said thermoplasticpolyurethane elastomer film and below a melting temperature of saidthermoplastic polyurethane elastomer film; (c) compressing the layers offilm in surface apposition to form an interface therebetween by applyingpressure from a die and from said welding platen to said thermoplasticpolyurethane elastomer film; (d) transmitting radio-frequency energy tothe layers of film while said thermoplastic polyurethane elastomer filmis under said pressure, welding the film layers at said interfacetherebetween forming a weld; and (e) cooling said weld of the at leasttwo layers of film, wherein said weld is free of holidays, pins holes,charring, burning, and wrinkles.
 2. A method of polyurethane filmwelding according to claim 1, wherein said weld has a strengthsubstantially equivalent to said thermoplastic polyurethane elastomerfilm in unwelded condition.
 3. A method of polyurethane film weldingaccording to claim 1, wherein said weld has a span of from about two toabout ten times the thickness of the polyurethane film.
 4. A method ofpolyurethane film welding according to claim 1, wherein said weld has aspan of about 3 to 10 times the thickness of the polyurethane film.
 5. Amethod of polyurethane film welding according to claim 1, wherein saidweld has integrity and continuity sufficient to constitute a biologicalbarrier.